Torque transmission joint and electric power steering apparatus

ABSTRACT

A shock-absorbing member comprises held sections located at a plurality of locations in a circumferential direction and comprising paired held sections and non-paired held sections, and is constructed to have a non-circular cylindrical shape in cross-section. Portions where outer-diameter side end sections of held sections that are adjacent to each other in the circumferential direction are made continuous by way of outer-diameter side cover sections, and portions where inner-diameter side end sections of held sections that are adjacent to each other in the circumferential direction are made continuous directly or by way of inner-diameter side cover sections, in an alternating sequence in the circumferential direction. Drive-side arm sections are placed between the non-paired held sections, driven-side arm sections are placed between the paired held sections, and the outer circumferential surfaces of the drive-side arm sections are covered by the outer-diameter side cover sections.

TECHNICAL FIELD

The present invention relates to a torque transmission joint that is assembled in various kinds of machinery and used for transmitting torque between a drive shaft and a driven shaft, and to an electric power steering apparatus in which this torque transmission joint is assembled that has a mechanism having an electric motor as an auxiliary power source, and that assists in operation of a steering wheel by an operator.

BACKGROUND ART

When applying a steering angle to steered wheels (normally the front wheels), electric power steering apparatuses are widely used, that use an electric motor as an auxiliary power source and that reduce the force required for an operator to operate the steering wheel. Electric power steering apparatuses having various structures are known, however, in all kinds of structures, auxiliary power from an electric motor is applied by way of a reduction gear to a rotating shaft that is rotated by operation of the steering wheel. Typically, a worm reducer is used as this reduction gear. In the case of an electric power steering apparatus that uses a worm reducer, a worm that is rotated and driven by an electric motor is geared with a worm wheel that rotates together with the rotating shaft, and the auxiliary power from the electric motor is transmitted to the rotating shaft by way of the worm and worm wheel. However, in the case of a worm reducer, unless various measures are taken, backlash that exists in the gear engagement section between the worm and worm wheel when changing the direction of rotation of the rotating shaft may cause an unpleasant noise called “gear rattle” to occur.

JP 2000-43739 (A), JP 2004-306898 (A) and JP 2006-513906 (A) disclose a structure in which the occurrence of this kind of gear rattle is suppressed by elastically pressing the worm toward the worm wheel using an elastic member such as a spring. FIG. 37 and FIG. 38 illustrate an example of an electric power steering apparatus disclosed in JP 2004-306898 (A). The front-end section of a steering shaft 2 that rotates as the steering wheel 1 is rotated is supported inside a housing 3 so as to be able to rotate freely. A worm wheel 4 is fastened to the front-end section of the steering shaft 2. On the other hand, a worm 5 has a worm shaft 6 and worm teeth 7 that are provided around the middle section in the axial direction of the worm shaft 6 and that are geared with the worm wheel 4. Both end sections in the axial direction of the worm shaft 6 that is rotated and driven by an electric motor 8 are supported inside the housing 3 by way of a pair of rolling bearings 9 a, 9 b, such as deep-groove ball bearings, so as to be able to rotate freely. Furthermore, a pressure piece 10 is fitted around a portion of the tip-end section of the worm shaft 6 that protrudes out further than the rolling bearing 9 a, and an elastic member such as a coil spring 11 is provided between the pressure piece 10 and the housing 3. The elastic force of the spring 11 that is transmitted to the worm shaft 6 by way of the pressure piece 10 pushes the worm 5 toward the worm wheel 4. With this kind of construction, backlash between the worm 5 and the worm wheel 4 is reduced, and the occurrence of gear rattle is suppressed.

In this conventional structure, the base-end section of the worm shaft is joined to the tip-end section of the output shaft 12 of the electric motor 8, and there is a possibility that gear rattle will occur in this joint section as well. In other words, in order that the tip-end section of the output shaft 12 and the base-end section of the worm shaft 6 are joined so as to be able to transmit torque, a spline hole 13 that is open on the base-end surface of the worm shaft 6 is formed on the base-end section of the worm shaft 6, and a spline shaft section 14 is formed on the tip-end section of the output shaft 12 such that the spline shaft section 14 spline-engages with the spline hole 13. As long as the spline shaft section 14 spline-engages with the spline hole 13 such that there are no gaps in the circumferential direction, gear rattle will not occur in the joint section between the tip-end section of the output shaft 12 and the base-end section of the worm shaft 6. However, in actuality, there is backlash in the spline engagement between the spline shaft section 14 and the spline hole 13. Particularly, in the structure such as illustrated in FIG. 38 for reducing backlash between the worm 5 and worm wheel 4, it is necessary to cause the worm shaft 6 to pivotally displace, so it is not possible to completely eliminate the backlash that exists between the spline shaft section 14 and the spline hole 13, and thus it is difficult to prevent the occurrence of gear rattle in the joint section between the tip-end section of the output shaft 12 and the base-end section of the worm shaft 6.

JP H03-73745 (U) and JP 4,523,721 (B2) disclose structure that prevents the occurrence of gear rattle in a joint section between a drive shaft and driven shaft by joining the end section of a drive shaft and the end section of a driven shaft by way of a torque transmission joint (shaft joint) that has a shock-absorbing member made of an elastic material. FIG. 39 and FIG. 40 illustrate a conventional torque transmission joint 15 that is disclosed in JP H03-73745 (U). The torque transmission joint 15 has: a metal drive-side transmission member 16 that is concentrically supported by the tip-end section of an output shaft 12 of an electric motor as a drive shaft; a metal driven-side transmission member 17 that is concentrically supported by the base-end section of a worm shaft 6 as a driven shaft; a rubber shock-absorbing member 18 that is provided between the drive-side transmission member 16 and the driven-side transmission member 17; and a steel ball 19.

The drive-side transmission member 16 has: a disk-shaped drive-side base section 20 that is supported by the tip-end section of the output shaft 12 so that relative rotation is not possible; and three drive-side arm sections 21 that are provided on the surface of the drive-side base section 20 that faces the driven-side transmission member 17 in a state such that these drive-side arm sections 21 are intermittently spaced in the circumferential direction and protrude out in the axial direction. On the other hand, the driven-side transmission member 17 has: a disk-shaped driven-side base section 22 that is supported by the base-end section of the worm shaft 6 so that relative rotation is not possible; and three driven-side arm sections 23 that are provided on the surface of the driven-side base section 22 that faces the drive-side transmission member 16 in a state such that these driven-side arm sections 23 are intermittently spaced in the circumferential direction and protrude out in the axial direction. Moreover, the shock-absorbing member 18 has: a hollow cylindrical section 24; and six held sections 25 that extend in the radial direction from the outer circumferential surface of the cylindrical section 24. In the assembled state of the torque transmission joint 15, the drive-side arm sections 21 and the driven-side arm sections 23 are arranged in an alternating sequence in the circumferential direction. The held sections 25 of the shock-absorbing member 18 are placed between the side surfaces in the circumferential direction of the drive-side arm sections 21 and the driven-side arm sections 23 that are adjacent to each other in the circumferential direction. Furthermore, the steel ball 19 is held between the tip-end surface of the output shaft 12 and the base-end surface of the worm shaft 6.

In the torque transmission joint 15, the rubber held sections 25 are held between the side surface in the circumferential direction of drive-side arm sections 21 and the driven-side arm sections 23 that are adjacent to each other in the circumferential direction. Therefore, there is no direct contact between the metal drive-side arm sections 21 and driven-side arm sections 23, and thus the occurrence of gear rattle is effectively prevented. Moreover, in this construction, during operation, thrust force that is transmitted between the output shaft 12 and the worm shaft 6 is transmitted by way of the steel ball 19. Therefore, because this thrust force is not transmitted to the shock-absorbing member 18, the durability of the shock-absorbing member 18 can be maintained over a long period of time.

However, in the structure of the torque transmission joint 15, errors in dimensions of the components, and assembly error cannot be effectively absorbed. For example, when there is so-called alignment error in which the positional relationship of the center axis of the output shaft 12 of the electric motor and the center axis of the worm shaft 6 does not coincide, this alignment error is absorbed by elastic deformation of part of the cylindrical section 24 and held sections 25 of the shock-absorbing member 18. Therefore, the more elastic deformation there is of the cylindrical section 24 of the shock-absorbing member 18, the larger the alignment error can be absorbed. However, in this structure, held sections 25 are arranged in the radial direction, and the side surfaces in the circumferential direction of the drive-side arm sections 21 and the driven-side arm sections 23 extend in the radial direction. That is to say, each of virtual planes containing the side surfaces in the circumferential direction passes through the center axis of the drive-side transmission member 16 and the driven-side transmission member 17. Therefore, when the output shaft 12 is rotated and driven and torque begins to be transmitted, a force that causes elastic contraction acts over the entire length of the held sections 25 that are located between the side surfaces in the circumferential direction of the front side in the direction of rotation of the drive-side arm sections 21 and the side surfaces in the circumferential direction of the rear sides in the direction of rotation of the driven-side arm sections 23. This makes a force in the pulling direction act on the cylindrical section 24, so it becomes difficult for elastic deformation to occur in the radial direction of the cylindrical section 24. Therefore, together with it becoming difficult to sufficiently absorb the alignment error between the output shaft 12 and the worm shaft 6, the surface pressure that occurs at part of the contact section between the outer circumferential surface 24 and the inner circumferential surfaces of the drive-side arm sections 21 and the driven-side arm sections 23 becomes very large, and friction resistance in that part increases, which could cause the overall transmission efficiency of the electric power steering apparatus to decrease.

Moreover, in the torque transmission joint 15, the held sections 25 of the shock-absorbing member 18 are arranged in the radial direction, so in the assembled state of the torque transmission apparatus 15, the shock-absorbing member 18 is only exposed to the outside from between the drive-side arm sections 21 and the driven-side arm sections 23 that are adjacent to each other in the circumferential direction. Therefore, it becomes difficult to visually check the shock-absorbing member 18, and thus a problem also occurs in that work efficiency of the inspection process in order to prevent assembly of the shock-absorbing member 18 from being forgotten is decreased.

JP 4,779,358 (B2) discloses structure in which the shock-absorbing member has three members that are stacked in the axial direction, however, in this structure as well, the held sections of the shock-absorbing member are arranged in the radial direction, so the problem described above is not solved.

RELATED LITERATURE Patent Literature

[Patent Literature 1] JP 2000-43739 (A)

[Patent Literature 2] JP 2004-306898 (A)

[Patent Literature 3] JP 2006-513906 (A)

[Patent Literature 4] JP H03-73745 (U)

[Patent Literature 5] JP 4,523,721 (B2)

[Patent Literature 6] JP 4,779,358 (B2)

SUMMARY OF INVENTION Problem to be Solved by Invention

Taking the situation above into consideration, it is the object of the present invention to provide a torque transmission joint that is able to effectively absorb error such as dimension error or assembly error of components, and that is also able to improve the work efficiency of the inspection process in order to prevent assembly of a shock-absorbing member from being forgotten, and to provide an electric power steering apparatus that has this torque transmission joint.

Means for Solving Problems

The torque transmission joint of the present invention has: a drive-side transmission member that is supported by the end section of a drive shaft, and is concentric with the drive shaft; a driven-side transmission member that is supported by the end section of a driven shaft that is arranged in series in the axial direction with the drive shaft, and is concentric with the driven shaft; and a shock-absorbing member that is made of an elastic material and is provided between the drive-side transmission member and the driven-side transmission member; and the torque transmission joint transmits torque between the end sections of the drive shaft and the driven shaft.

The drive-side transmission member has: a drive-side base section that is supported by the end section of the drive shaft; and a plurality of drive-side arm sections that are provided on the surface of the drive-side base section that faces the driven-side transmission member, and are provided intermittently in the circumferential direction in a state so as to protrude out in the axial direction. Moreover, the driven-side transmission member has: a driven-side base section that is supported by the end section of the driven shaft; and a plurality of driven-side arm sections that are provided on the surface of the driven-side base section that faces the drive-side transmission member, and are provided intermittently in the circumferential direction in a state so as to protrude out in the axial direction.

The shock-absorbing member has combined held sections that each have paired flat plate-shaped held sections, and that are located at plural locations in the circumferential direction, and the shock-absorbing member is constructed so as to have a non-circular cylindrical shape in the cross section by arranging portions where the outer-diameter side end sections of the held sections that are adjacent to each other in the circumferential direction are made continuous by way of the outer-diameter side cover sections, and portions where the inner-diameter side end sections of the held sections that are adjacent to each other in the circumferential direction are made continuous directly or by way of the inner-diameter side cover sections, in an alternating sequence in the circumferential direction.

The drive-side arm sections and the driven-side arm sections are arranged in an alternating sequence in the circumferential direction, and the held sections are arranged between the side surfaces in the circumferential direction of the drive-side arm sections and the driven-side arm sections that are adjacent to each other in the circumferential direction.

Ones of the drive-side arm sections and the driven-side arm sections are placed between the paired held sections that constitute the combined held sections, and the others of the drive-side arm sections and the driven-side arm sections are placed between the combined held sections that are adjacent to each other in the circumferential direction, and the outer circumferential surfaces of either of the drive-side arm sections or the driven-side arm sections are covered by the outer-diameter side cover sections.

Preferably, the paired held sections that constitute the combined held sections each have a mirror symmetry about an imaginary plane that passes through the center axis of the shock-absorbing member, and are inclined in a direction toward the imaginary plane with respect to the radial direction as going toward the outside in the radial direction, and of the paired side surfaces of the drive-side arm sections, the side surfaces positioned in the front in the direction of rotation of the drive shaft are inclined in a direction toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction.

Preferably, the shock-absorbing member is formed using two or more kinds of shock-absorbing pieces having different elasticity, and the shock-absorbing pieces have held pieces that, when layered in the axial direction, form the held sections; and cover pieces that, when layered in the axial direction, form the outer-diameter side cover sections.

Moreover, preferably, of the shock-absorbing pieces of the shock-absorbing member, the side surfaces in the circumferential direction of the held pieces of the shock-absorbing piece that is manufactured using a material that elastically deforms more easily than the other shock-absorbing pieces protrude further in the circumferential direction than the side surfaces in the circumferential direction of the held pieces of the other shock-absorbing pieces.

Preferably, the shock-absorbing pieces of the shock-absorbing member are joined together by engagement between an engaging section and an engaged section that are provided on the shock-absorbing pieces.

Preferably, a damper member for absorbing part of the thrust force that acts between the drive shaft and driven shaft and transmitting the remaining thrust force is provided on the inside of the shock-absorbing member. In this case, preferably, the damper member is integrally formed with at least one of the shock-absorbing pieces of the shock-absorbing member.

Preferably, the combined held sections are provided at four locations that are uniformly spaced in the circumferential direction, and the cross-sectional shape of the shock-absorbing member is a cross cylindrical shape.

The electric power steering apparatus of the present invention has: a housing that is supported by a fixed portion; a rotating steering shaft that rotates as a steering wheel is rotated and applies a steering angle to steered wheels; a worm wheel that is supported by part of the rotating steering shaft so as to be concentric with the rotating steering shaft, and rotates together with the rotating steering shaft; a worm that has a worm shaft, both end sections in the axial direction thereof being supported inside the housing by bearings so as to be able to rotate freely, and worm teeth that are provided around the middle section in the axial direction of the worm shaft and that gear with the worm wheel; and an electric motor; and the torque transmission joint of the present invention is provided between the output shaft of the electric motor and the worm shaft such that the torque transmission joint can transmit the torque between the output shaft and the worm shaft.

Effect of Invention

With the torque transmission joint and electric power steering apparatus of the present invention, it is possible to effectively absorb error such as dimension error or assembly error of components, and it is possible to improve the work efficiency of the inspection process in order to prevent assembly of the shock-absorbing member from being forgotten.

In other words, in the present invention, when the transmission of torque is started by rotating and driving the drive shaft, forces inward in the radial direction of the shock-absorbing member acts on the held sections that are held between side surfaces in the circumferential direction on the front side in the direction of rotation of the drive-side arm sections and the side surface in the circumferential direction on the rear side in the direction of rotation of the driven-side arm sections. As a result, portions near the inner-diameter side end sections of the held sections can be bent inward in the radial direction, and the shock-absorbing member is in a state in which elastic deformation can occur easily. Particularly, when the inner-diameter side end sections of the held sections are not continuous in the circumferential direction, and the portions on the inner-diameter side of the shock-absorbing member are not continuous in the circumferential direction, it is possible to put the shock-absorbing member in a state in which elastic deformation occurs more easily. With this kind of construction, alignment error that occurs between the drive shaft and the driven shaft can be sufficiently absorbed, and it is possible to improve the transmission efficiency of the overall system of the electric power steering apparatus.

Moreover, in the present invention, the outer-diameter side cover sections that make the outer-diameter side end sections of the held sections of the shock-absorbing member continuous, cover the outer circumferential surfaces of the arm sections of one of either the drive-side arm sections or the driven-side arm sections, and when the torque transmission joint is assembled, the surface area of the portions exposed to the outside is sufficiently large. Therefore, it is possible to improve the work efficiency of the inspection process in order to prevent assembly of the shock-absorbing member from being forgotten.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional drawing of the major parts of an electric power steering apparatus in which a torque transmission joint of a first example of a first embodiment of the present invention is assembled.

FIG. 2 is a perspective drawing that schematically illustrates the torque transmission joint that has been removed from the electric power steering apparatus illustrated in FIG. 1.

FIG. 3 is an enlarged cross-sectional drawing of section A-A in FIG. 1.

FIG. 4 is an end view illustrating a shock-absorbing member that has been removed from the torque transmission joint illustrated in FIG. 2.

FIG. 5 is an exploded perspective drawing that schematically illustrates a second example of the first embodiment of the present invention.

FIG. 6 is a cross-sectional drawing of the second example of the first embodiment, and is similar to FIG. 3.

FIG. 7 is an end view illustrating a shock-absorbing member that has been removed from the torque transmission joint illustrated in FIG. 5.

FIG. 8 is an exploded perspective drawing that schematically illustrates a third example of the first embodiment of the present invention.

FIG. 9 is a cross-sectional drawing of the third example of the first embodiment, and is similar to FIG. 3.

FIG. 10 is an end view illustrating a shock-absorbing member that has been removed from the torque transmission joint illustrated in FIG. 8.

FIG. 11 is an exploded perspective drawing that schematically illustrates a fourth example of the first embodiment of the present invention.

FIG. 12 is an end view illustrating a shock-absorbing member that has been removed from the torque transmission joint illustrated in FIG. 11.

FIG. 13 is a partial end views of three shock-absorbing pieces of the shock-absorbing member illustrated in FIG. 12 that are vertically arranged.

FIG. 14 is an end view of a shock-absorbing member of a torque transmission joint of a fifth example of the first embodiment of the present invention.

FIG. 15 is a drawing similar to FIG. 13 of shock-absorbing pieces of the shock-absorbing member illustrated in FIG. 14.

FIG. 16 is an end view of a shock-absorbing member of a torque transmission joint of a sixth example of the first embodiment of the present invention.

FIG. 17 is a partial end view of a shock-absorbing piece that is arranged in the center in the axial direction of the shock-absorbing member illustrated in FIG. 16.

FIG. 18 is an exploded perspective drawing that schematically illustrates a torque transmission joint of a seventh example of the first embodiment of the present invention.

FIG. 19 is an exploded perspective drawing that schematically illustrates a torque transmission joint of an eighth example of the first embodiment of the present invention.

FIG. 20 is cross-sectional drawing of an electric power steering apparatus in which a torque transmission joint of an example of a second embodiment of the present invention is assembled.

FIG. 21 is perspective drawing illustrating a torque transmission joint that has been removed from the electric power steering apparatus illustrated in FIG. 20.

FIG. 22 is a perspective drawing of the torque transmission joint illustrated in FIG. 21 in a state as seen from another direction.

FIG. 23 is an exploded perspective drawing of the torque transmission joint illustrated in FIG. 21.

FIG. 24 is an exploded perspective drawing of the torque transmission joint illustrated in FIG. 21 in a state as seen from another direction.

FIG. 25 is an enlarged cross-sectional drawing of section B-B in FIG. 20.

FIG. 26 is an end view of the drive-side transmission member that has been removed from the torque transmission joint illustrated in FIG. 21 as seen from the tip-end side of the drive-side arm sections thereof.

FIG. 27 is an end view of the driven-side transmission member that has been removed from the torque transmission joint illustrated in FIG. 21 as seen from the tip-end side of the driven-side arm sections thereof.

FIG. 28 is an end view of the shock-absorbing member of the torque transmission joint illustrated in FIG. 21.

FIG. 29 is a perspective drawing of the shock-absorbing member illustrated in FIG. 28.

FIG. 30 is a perspective drawing of the shock-absorbing member illustrated in FIG. 28 as seen from another direction.

FIG. 31 is a cross-sectional drawing of section C-C in FIG. 28.

FIG. 32 is an exploded perspective drawing of the shock-absorbing member illustrated in FIG. 28.

FIG. 33 is an exploded perspective drawing of the shock-absorbing member illustrated in FIG. 28 as seen from another direction.

FIG. 34 is an end view that illustrates an inside shock-absorbing piece that was removed from the shock-absorbing member illustrated in FIG. 28.

FIG. 35 is an end view that illustrates an outside shock-absorbing piece that was removed from the shock-absorbing member illustrated in FIG. 28.

FIGS. 36A and 36B are drawings illustrating two other examples of shapes of the swollen sections that can be applied to the shock-absorbing member of the torque transmission joint of the present invention.

FIG. 37 is a partial vertical cross-sectional side view that illustrates an example of a steering apparatus for an automobile.

FIG. 38 is an enlarged cross-sectional drawing of section D-D in FIG. 37, and illustrates an example of a conventional electric power steering apparatus.

FIG. 39 is an exploded perspective drawing that illustrates a conventional torque transmission joint.

FIG. 40 is a cross-sectional drawing of the conventional torque transmission joint of FIG. 39, and is similar to FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Example of First Embodiment

FIG. 1 to FIG. 4 illustrate a first example of a first embodiment of the present invention. The electric power steering apparatus of this example has: a housing 3 that is supported by a fixed portion; a steering shaft (rotating shaft for steering) 2 that is provided so as to be able to rotate freely with respect to the housing 3 and that applies a steering angle to the steered wheels by rotating as the steering wheel 1 rotates; a worm wheel 4 that is supported inside the housing 3 by part (front-end section) of the steering shaft 2 so as to be concentric with the steering shaft 2 and so as to rotate together with the steering shaft 2; a worm 5 that has a worm shaft 6 a that is supported by bearings on both end sections in the axial direction so as to be able to rotate freely with respect to the housing 3, and worm teeth 7 that are provided around the middle section in the axial direction of the worm shaft 6 a and that gear with the worm wheel 4; and an electric motor 8 for rotating and driving the worm 5. In this example, a torque transmission joint 15 a, to which the present invention is applied, is provided between the tip-end section of the output shaft 12 a of the electric motor 8 and the base-end section of the worm shaft 6 a of the worm 5, and is able to transmit torque from the output shaft 12 a to the worm shaft 6 a. Except for the torque transmission joint 15 a, the construction and function of the electric power steering apparatus is the same as a conventional electric power steering apparatus.

The torque transmission joint 15 a of this example has: a drive-side transmission member 16 a that is supported by the tip-end section of the output shaft 12 a as a drive shaft, so as to be concentric with the tip-end section; a driven-side transmission member 17 a that is supported by the base end section of the worm shaft 6 a as a driven-side shaft, so as to be concentric with the base-end section; a shock-absorbing member 18 a that is provided between the drive-side transmission member 16 a and the driven-side transmission member 17 a; and a damper member 26.

The drive-side transmission member 16 a is made of metal and has a drive-side base section 20 a and four drive-side arm sections 21 a. The drive-side base section 20 a has a disk shape and is provided with a drive-side serration hole 27 that is formed in the center section thereof and engages with a male serration section that is formed around the outer circumferential surface on the tip-end section of the output shaft 12 a by way of serration engagement. The drive-side arm sections 21 a are provided in portions near the outer-diameter on a surface of the drive-side base section 20 a that faces the driven-side transmission member 17 a such that the drive-side arm sections 21 a are arranged intermittently in the circumferential direction (shifted at a phase of 90 degrees), and so as to protrude out in the axial direction.

On the other hand, the driven-side transmission member 17 a is made of metal and has a driven-side base section 22 a and four driven-side arm sections 23 a. The driven-side base section 22 a has a disk shape, and is provided with a driven-side serration hole 27 that is formed in the center section thereof and engages with a male serration section that is formed around the outer circumferential surface on the base-end section of the worm shaft 6 a by way of serration engagement. The driven-side arm sections 23 a are provided in portions near the outer diameter on a surface of the driven-side base section 22 a that faces the drive-side transmission member 16 a such that the driven-side arm sections 23 a are arranged intermittently in the circumferential direction (shifted at a phase of 90 degrees), and so as to protrude out in the axial direction. The dimension in the axial direction of the drive-side arm sections 21 a and the dimension in the axial direction of the driven-side arm sections 23 a are the same.

In this example, paired side surfaces 29 a, 29 b in the circumferential direction 29 a, 29 b of the drive-side arm section 21 a are not arranged in the radial direction, but are arranged so as to incline with respect to the radial direction. More specifically, when the direction of rotation of the output shaft 12 a is clockwise in FIG. 3, the side surfaces 29 a, that are ones of the side surfaces 29 a, 29 b in the circumferential direction, and that are on the front side in the direction of rotation, incline in a direction toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction (the direction toward the rear in the direction of rotation as going toward the inside in the radial direction). On the other hand, when the direction of rotation of the output shaft 12 a is counterclockwise in FIG. 3, the side surfaces 29 b, that are the others of the side surfaces 29 a, 29 b in the circumferential direction, and that are on the front side in the direction of rotation, incline in a direction toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction (the direction toward the rear in the direction of rotation as going toward the inside in the radial direction). In this example, the angle that is formed by the paired side surfaces 29 a, 29 b in the circumferential direction of the drive-side arm section 21 a is less than 90 degrees (is about 75 degrees in the example in the figure).

Moreover, paired side surfaces 30 a, 30 b in the circumferential direction of the driven-side arm section 23 a are also not arranged in the radial direction, but are arranged so as to incline with respect to the radial direction. More specifically, when the direction of rotation of the output shaft 12 a is clockwise in FIG. 3, the side surfaces 30 a, that are ones of the side surfaces 30 a, 30 b in the circumferential direction, and that are on the front side in the direction of rotation, incline in a direction toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. On the other hand, when the direction of rotation of the output shaft 12 a is counterclockwise in FIG. 3, the side surface 30 b, that are the others of the side surfaces 30 a, 30 b in the circumferential direction, and that are on the front side in the direction of rotation, incline in a direction toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. In other words, in this example, the spacing in the circumferential direction of the paired side surfaces 30 a, 30 b in the circumferential direction of the driven-side arm section 23 a becomes a little larger as going toward the outside in the radial direction.

The shock-absorbing member 18 a is integrally formed by injection molding using an elastic material such as an elastomer like rubber or vinyl, a synthetic resin or the like, and has a total of eight held sections 25 a, 25 b (four held sections 25 a and four held sections 25 b), four outer-diameter side cover sections 31 and four inner-diameter side cover sections 32.

The held sections 25 a, 25 b are all flat-plate shaped (in the free state, are straight with a fixed plate thickness), and are arranged between side surfaces 29 a, 30 b, 30 a, 29 b in the circumferential direction of the drive-side arm sections 21 a and the driven-side arm sections 23 a that are adjacent to each other in the circumferential direction. Particularly, paired held sections 25 a, 25 b that are adjacent in the circumferential direction each have a mirror symmetry about an imaginary plane passing through the center axis of the shock-absorbing member 18 a (planes on the chain lines α, β, γ, δ in FIG. 4), and are inclined in a direction toward the imaginary plane with respect to the radial direction as going toward the outside in the radial direction. In other words, the held sections 25 a, 25 b are arranged not in the radial direction, but so as to incline with respect to the radial direction. Therefore, between the paired held sections 25 a, 25 b, the inclination angles are the same, but the directions of inclination are opposite. Moreover, in this example, the paired held sections 25 a, 25 b incline in a direction toward each other as going toward the inside in the radial direction. Combined held sections 33 that are formed by the paired held sections 25 a, 25 b are located at four locations that are uniformly spaced in the circumferential direction.

The outer-diameter side cover sections 31 and the inner-diameter side cover sections 32 are curved in a partial cylindrical shape. The inner-diameter side cover section 32 makes the inner-diameter side end sections of the paired held sections 25 a, 25 b that are adjacent to each other in the circumferential direction of the combined held sections 33 continuous. Moreover, the outer-diameter side cover section 31 makes the outer-diameter side end sections of the non-paired held sections 25 a, 25 b that are adjacent to each other but pertain to the different combined held sections 33 continuous. As a result, portions where the outer-diameter side end sections of the held sections 25 a, 25 b that are adjacent to each other in the circumferential direction are made continuous by way of the outer-diameter side cover section 31, and portions where the inner-diameter side end sections of the held sections 25 a, 25 b that are adjacent to each other in the circumferential direction are made continuous by way of the inner-diameter side cover section 32 are arranged in an alternating sequence in the circumferential direction. By employing this kind of construction, the cross-sectional shape of the shock-absorbing member 18 a has a cross cylindrical shape.

The shock-absorbing member 18 a, the drive-side arm sections 21 a and the driven-side arm sections 23 a are combined as illustrated in FIG. 3. More specifically, the driven-side arm sections 23 a are each located between the paired held sections 25 a, 25 b of the combined held sections 33. Moreover, the drive-side arm sections 21 a are each located between the combined held sections 33 that are adjacent to each other in the circumferential direction (between the non-paired held sections 25 a, 25 b that are adjacent to each other in the circumferential direction but pertain to the different combined held sections 33). As a result, the outer circumferential surfaces of the drive-side arm sections 21 a are covered by the outer-diameter side cover sections 31 of the shock-absorbing member 18 a, and the inner circumferential surfaces of the driven-side arm sections 23 a are covered by the inner-diameter side cover sections 32. In this assembled state, the paired side surfaces 29 a, 29 b in the circumferential direction of the drive-side arm section 21 a, and the paired side surfaces 30 a, 30 b in the circumferential direction of the driven-side arm sections 23 a come in contact over the entire surface or face through a minute gap over the entire surface of the side surfaces in the circumferential direction of the held sections 25 a, 25 b with respect to the circumferential direction.

The damper member 26 is provided on the inside of the shock-absorbing member 18 a between the drive-side arm sections 16 a and the driven-side arm sections, and has a metal circular column-shaped support-column section 34, and a main damper section 35 that fits around the middle section in the axial direction of the support-column section 34 so as to be able to displace in the axial direction. The end sections of the support-column section 34 loosely fit inside the drive-side serration hole 27 and the driven-side serration hole 28. Moreover, the main damper section 35 is made of an elastic material such as rubber, synthetic resin or the like, and has a dimension in the axial direction that is greater than the dimension in the axial direction of the shock-absorbing member 18 a, drive-side arm sections 21 a and driven-side arm sections 23 a. The main damper section 35 is inserted into the inner-diameter side of the inner-diameter side cover sections 32 of the shock-absorbing member 18 a, and held in the axial direction between surfaces of the drive-side base section 20 a and the driven-side base section 22 a that face each other. In this example, gaps are provided between both end surfaces of the support-column section 34 and the tip-end surface of the output shaft 12 and the base-end surface of the worm shaft 6 a having a size that is large enough to disappear when the main damper unit 35 elastically deforms a certain amount in the axial direction.

In the case of the torque transmission joint 15 a and electric power steering apparatus of this example, error such as dimension error and assembly error of components can be effectively absorbed. In other words, in this example, when transmission of torque begins by rotating and driving the output shaft 12 a of the electric motor 8, a force inward in the radial direction of the shock-absorbing member 18 a acts on the held sections 25 a, 25 b that are held between the side surfaces 29 a, 29 b in the circumferential direction of the drive-side arm sections 21 a and the side surfaces 30 b, 30 a in the circumferential direction of the driven-side arm sections 23 a.

For example, when the transmission of torque is started by rotating and driving the output shaft 12 a in the clockwise direction, four held sections 25 a of the shock-absorbing member 18 a are held between the side surfaces 29 a in the circumferential direction on the front side in the direction of rotation of the drive-side arm sections 21 a and the side surfaces 30 b in the circumferential direction on the rear side in the direction of rotation of the driven-side arms section 23 a. In this case, the side surfaces 29 a in the circumferential direction of the drive-side arm sections 21 a incline in the direction toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction, which causes the held sections 25 a to be gradually compressed and elastically deform from the portion on the outer-diameter side toward the portion on the inner-diameter side. Then, as illustrated by the solid arrows in FIG. 3, forces inward in the radial direction of the shock-absorbing member 18 a act on the held sections 25 a.

On the other hand, when the transmission of torque begins by rotating and driving the output shaft 12 a in the counterclockwise direction, four held sections 25 b of the shock-absorbing member 18 a are held between the side surfaces 29 b in the circumferential direction on the front side in the direction of rotation of the drive-side arm sections 21 a and the side surfaces 30 a in the circumferential direction on the rear side in the direction of rotation of the driven-side arm sections 23 a. In this case, the side surfaces 29 b in the circumferential direction of the drive-side arm sections 21 a incline in the direction toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction, which causes the held sections 25 b to be gradually compressed and elastically deform from the portion on the outer-diameter side toward the portion on the inner-diameter side. Then, as illustrated by the broken arrows in FIG. 3, forces inward in the radial direction of the shock-absorbing member 18 a act on the held sections 25 b.

Therefore, when the output shaft 12 a is rotated and driven clockwise in FIG. 3, the portions near the inner-diameter side end sections of the held sections 25 a can be bent inward in the radial direction (into weakly constrained state), and when the output shaft 12 a is rotated and driven counterclockwise in FIG. 3, the portions near the inner-diameter side end sections of the held sections 25 b can be bent inward in the radial direction (into weakly constrained state). Therefore, in either case, the shock-absorbing member 18 a is in a state in which elastic deformation is easier than in the conventional construction. Particularly, in this example, the inner-diameter side end sections of the held sections 25 a, 25 b are not continuous in the circumferential direction as in the conventional construction, and the inner-diameter side portions of the shock-absorbing member 18 a are not continuous in the circumferential direction, so the shock-absorbing member 18 a can be put into a state in which elastic deformation is easier. As a result of this kind of construction, error that occurs between the output shaft 12 a and the worm shaft 6 a can be sufficiently absorbed, and it is possible to improve the transmission efficiency of the overall system of the electric power steering apparatus. However, as long as the feature of the present invention, which is causing an inward force in the radial direction of the shock-absorbing member 18 a to act on the held sections 25 a, 25 b that are held between the side surfaces in the circumferential direction that are located on the front in the direction of rotation of the output shaft 12 a of the drive-side arm sections 21 a, and the side surfaces in the circumferential direction that are located on the rear in the direction of rotation of the output shaft 12 of the driven-side arm sections 23 a, can be obtained, the shape of the shock-absorbing member is not limited to the construction of this example.

Moreover, in this example, it is possible to improve the work efficiency of the inspection process in order to prevent the assembly of the shock-absorbing member 18 d from being forgotten. In other words, in a state in which the outer-diameter side cover sections 31 that are continuous with the outer-diameter side end sections of the held sections 25 a, 25 b of the shock-absorbing member 18 a covers the outer circumferential surfaces of the drive-side arm sections 21 a, and the torque transmission joint 15 a is assembled, the surface area of the portions that are exposed to the outside is sufficiently large. Therefore, it is possible to easily perform a visual check of the shock-absorbing member 18 a, and to improve the work efficiency of the inspection process in order to prevent the assembly of the shock-absorbing member 18 d from being forgotten.

In this example, the held sections 25 a, 25 b that are made of an elastic material are located between the side surfaces in the circumferential direction of the drive-side arm sections 21 a and the driven-side arm sections 23 a that are adjacent to each other in the circumferential direction, so the occurrence of gear rattle is effectively prevented. Furthermore, when a thrust force acts between the output shaft 12 a and the worm shaft 6 a, the main damper section 35 of the damper member 25 elastically deforms and contracts between the surfaces of the drive-side base section 20 a and driven-side base section 22 a that face each other, which absorbs part of the thrust force, and transmits the remaining thrust force. Therefore, it is possible to reduce the thrust force that is transmitted between the output shaft 12 a and the worm shaft 6 a. Moreover, this thrust force is effectively prevented from being transmitted to the shock-absorbing member 18 a, making it possible to maintain the durability of the shock-absorbing member 18 a over a long period of time.

Second Example of First Embodiment

FIG. 5 to FIG. 7 illustrate a second example of the first embodiment of the present invention. The torque transmission joint 15 b of this example also has: a drive-side transmission member 16 b, a driven-side transmission member 17 b, a shock-absorbing member 18 b and a damper member 26.

In this example, the four drive-side arm sections 21 b that are provided on the drive-side transmission member 16 b are such that the inclination angles with respect to the radial direction of the paired side surfaces 29 c, 29 d in the circumferential direction of each of the drive-side arm sections 21 b are increased by the same amount when compared with the first example of the first embodiment. In other words, when the output shaft 12 a is rotated and driven, the side surface 29 c (29 d) in the circumferential direction that is on the front side in the direction of rotation is inclined more toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. The angle made between the paired side surfaces 29 c, 29 d in the circumferential direction is 90 degrees (right angle), and the cross-sectional shape of the drive-side arm sections 21 b is a right triangle shape.

The four driven-side arm sections 23 that are provided on the driven-side transmission member 17 b are such that the inclination angles in the radial direction of the paired side surfaces 30 c, 39 d in the circumferential direction are increased by the same amount when compared with the first example of the first embodiment. In other words, when the output shaft 12 a is rotated and driven, the side surfaces 30 c (30 d) in the circumferential surface that are the front side in the direction of rotation are inclined more toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. The paired side surfaces 30 c, 30 d in the circumferential direction are arranged parallel with each other, and the cross-sectional shape of the driven-side arm sections 23 b is a rectangular shape.

Furthermore, the combined held sections 33 a of the shock-absorbing member 18 b are also such that the inclination angles with respect to the radial direction of each of the paired held sections 25 c, 25 d are increased by the same amount when compared with the first example of the first embodiment. In other words, when the output shaft 12 a is rotated and driven, the held section 25 c (25 d) that is the front side in the direction of rotation is inclined more toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. In this example, the paired held sections 25 c, 25 d are arranged parallel with each other. Moreover, the outer-diameter side end sections of each of the paired held sections 25 c, 25 d that are adjacent to each other in the circumferential direction of the combined held section 33 a are continuous by way of an outer-diameter side cover section 31 a, which has a flat plate shape (a straight shape such that in the free state the plate thickness is fixed), and the inner-diameter side end sections of each of the non-paired held sections 25 c, 25 d that are adjacent to each other in the circumferential direction but pertain to the different combined held sections 33 a are made to be directly continuous. As a result of this kind of construction, the cross-sectional shape of the shock-absorbing member is a cross cylindrical shape.

The shock-absorbing member 18 b and the drive-side arm sections 21 b and the driven-side arm sections 23 b are assembled as illustrated in FIG. 6. More specifically, the driven-side arm sections 23 b are each located between the paired held sections 25 c, 25 d of the combined held sections 33 a. Moreover, the drive-side arm sections 21 b are each located between the combined held sections 33 a that are adjacent to each other in the circumferential direction (between the non-paired held sections 25 c, 25 d that are adjacent to each other in the circumferential direction but pertain to the different combined held sections 33 a). As a result, the outer circumferential surfaces of the driven-side arm sections 23 b are covered by the outer-diameter side cover sections 31 a of the shock-absorbing member 18 b, and the inner-diameter side end edges of the drive side arm sections 21 b are covered by the continuous sections between the inner-diameter side end edges of the held sections 25 c, 25 d.

In this example, when the output shaft 12 a is rotated and driven, the forces inward in the radial direction of the shock-absorbing member 18 b that act on the held sections 25 c (25 d) as illustrated by the solid arrows in FIG. 6 can be increased when compared with the case of the first example of the first embodiment. Therefore, the shock-absorbing member 18 a can further be put into a state in which elastic deformation is easier. Consequently, with the construction of this example, it is possible to effectively absorb error such as dimension error or assembly error of components. The other construction and effects are the same as in the first example of the first embodiment.

Third Example of First Embodiment

FIG. 8 to FIG. 10 illustrate a third example of the first embodiment of the present invention. The torque transmission joint 15 c of this example also has: a drive-side transmission member 16 c, a driven-side transmission member 17 c, a shock-absorbing member 18 c and a damper member 26.

In this example, the four drive-side arm sections 21 c that are provided on the drive-side transmission member 16 c are such that the inclination angles with respect to the radial direction of the paired side surfaces 29 e, 29 f in the circumferential direction of the drive-side arm sections 21 c are decreased by the same amount when compared with the first example of the first embodiment. In other words, when the output shaft 12 a is rotated and driven, the side surface 29 e (29 f) in the circumferential direction that is on the front side in the direction of rotation is inclined less toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. In the example in the figure, the angle made between the paired side surfaces 29 e, 29 f in the circumferential direction is approximately 60 degrees.

The four driven-side arm sections 23 c that are provided on the driven-side transmission member 17 c are also such that the inclination angles in the radial direction of the paired side surfaces 30 e, 30 f in the circumferential direction of each driven-side arm sections 23 c are decreased by the same amount when compared with the first example of the first embodiment. In other words, when the output shaft is rotated and driven, the side surfaces 30 e (30 f) in the circumferential direction that are on the front side in the direction of rotation are inclined less toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction.

Furthermore, the combined held sections 33 b of the shock-absorbing member 18 c are also such that the inclination angles with respect to the radial direction of the paired held sections 25 e, 25 f are decreased by the same amount when compared with the first example of the first embodiment. In other words, when the output shaft 12 a is rotated and driven, the held sections 25 e (25 f) that are on the front side in the direction of rotation are inclined less toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. The outer-diameter side end sections of the paired held sections 25 e, 25 f that are adjacent to each other in the circumferential direction of the combined held sections 33 b are continuous by way of the outer-diameter side cover sections 31 b that have a partial cylindrical shape. Moreover, the non-paired held sections 25 e, 25 f that are adjacent to each other in the circumferential direction but pertain to the different combined held sections 33 b are continuous by way of the inner-diameter side cover sections 32 a that have a partial cylindrical shape. As a result of this kind of construction, the cross-sectional shape of the shock-absorbing member 18 c is a cross cylindrical shape.

The shock-absorbing member 18 c and the drive-side arm sections 21 c and the driven-side arm sections 23 c are assembled as illustrated in FIG. 9. More specifically, the driven-side arm sections 23 c are each arranged between the paired held sections 25 e, 25 f of the combined held section 33 b. Moreover, the drive-side arm sections 21 c are each arranged between the combined held sections 33 b that are adjacent to each other in the circumferential direction (between the non-paired held sections 25 e, 25 f that are adjacent to each other in the circumferential direction but pertain to the different combined held sections 33 b). As a result, the outer circumferential surfaces of the driven-side arm sections 23 c are covered by the outer-diameter side cover sections 31 b of the shock-absorbing member 18, and the inner circumferential surfaces of the drive-side arm sections 21 c are covered by the inner-diameter side cover sections 32 a.

In this example, when the outer shaft 12 a is rotated and driven, the forces that act inward in the radial direction of the shock-absorbing member 18 c on the held sections 25 e (25 f) as illustrated by the solid arrows in FIG. 9 are smaller than in the first example of the first embodiment. Therefore, it becomes more difficult for the shock-absorbing member 18 c to elastically deform than in the case of the first example of the first embodiment, however, when compared with the conventional construction, sufficient elastic deformation is possible. Consequently, in this example as well, it is possible to effectively absorb error such as dimension error or assembly error of components. Moreover, the outer-diameter side cover sections 31 b cover the outer circumferential surfaces of the driven-side arm sections 23 c that have a shorter length dimension in the circumferential direction than the drive-side arm sections 21 c, so the circumferential length of the shock-absorbing member 18 c can be made to be shorter. Therefore, it is possible to reduce the cost of the shock-absorbing member 18 c. The other construction and effects are the same as in the first example of the first embodiment.

Fourth Example of First Embodiment

FIG. 11 to FIG. 13 illustrate a fourth example of the first embodiment of the present invention. The feature of this example is that the shock-absorbing member 18 d of the torque transmission joint 15 d is constructed by layering a plurality of shock-absorbing pieces 36, 36 a in the axial direction instead of being integrally formed in one piece.

In this example, the shock-absorbing member 18 d is constructed by layering in the axial direction three shock-absorbing pieces 36, 36 a that have a shape in which the shock-absorbing member 18 b that was used in the second example of the first embodiment is divided into three (three slices) in the axial direction. Each of the shock-absorbing pieces 36, 36 a are layered in the axial direction and have: held pieces 37 a, 37 b (four held pieces 37 a and four held pieces 37 b) that form held sections 25 c, 25 d in the layered state in the axial direction, and outer-diameter side cover pieces 38 that form outer-diameter side cover sections 31 a in the layered state in the axial direction.

In this example, the shock-absorbing pieces 36 a that are arranged in the center in the axial direction are formed using a material that elastically deforms more easily than the pair of shock-absorbing pieces 36 that are arranged on both sides in the axial direction. More specifically, the shock-absorbing pieces 36 a are manufactured using a material that elastically deforms easily such as rubber or an elastomer, and the shock-absorbing pieces 36 are manufactured using a synthetic resin such as a polyacetal resin or polyamide resin for which elastic deformation is more difficult than rubber or an elastomer.

Moreover, one each of swollen sections 39 a, 39 a that protrude out in the circumferential directions are provide for each held pieces 37 a, 37 b of the shock-absorbing pieces 36 a that are manufactured using a material that elastically deforms easily. In this example, the cross-sectional shape of these swollen sections 39 a, 39 b is a right triangular shape, such that the side of the swollen sections 39 a, 39 b with the large protruding amount in the circumferential direction is arranged on the outer-diameter side of the held pieces 37 a, 37 b. When the shock-absorbing member 18 d, and the drive-side arm sections 21 b and the driven-side arm sections 23 b are assembled, part of the swollen sections 39 a, 39 b are elastically compressed between the side surfaces 29 c, 29 d in the circumferential direction of the drive-side arm sections 21 b and the side surfaces 30 c, 30 d in the circumferential direction of the driven-side arm sections 23 b.

In this example, when transmission of torque begins, first, the held pieces 37 a, 37 b of the shock-absorbing pieces 26 a that are arranged in the center in the axial direction and that are manufactured using a material that elastically deforms easily are held between the side surfaces 29 c, 29 d in the circumferential direction of the drive-side arm sections 21 b and the side surfaces 30 c, 30 d in the circumferential direction of the driven-side arm sections 23 b. Then, after the held pieces 37 a, 37 b (swollen sections 39 a, 39 b) of the shock-absorbing pieces 36 a have elastically deformed by a specified amount, the held pieces 37 a, 37 b of the shock-absorbing pieces 36 that are arranged on both sides in the axial direction are held. Therefore, the timing at which the held pieces 37 a, 37 b of the shock-absorbing pieces 36, 36 a are held differs between the plurality of shock-absorbing pieces 36, 36 a. Consequently, from the instant when torque transmission begins, the damper effect that prevents large torque from being transmitted can be increased.

Furthermore, when the shock-absorbing member 18 d is assembled, by providing the swollen sections 39 a, 39 b, it is possible to give the shock-absorbing 18 d interference with respect to the drive-side transmission member 16 b and driven-side transmission member 17 b. Therefore, the shock-absorbing member 18 d is effectively prevented from becoming loose with respect to the drive-side transmission member 16 b and the driven-side transmission member 17 b, and thus it is possible to stably transmit torque. The other construction and effects are the same as in the second example of the first embodiment.

Fifth Example of First Embodiment

FIG. 14 and FIG. 15 illustrate a fifth example of the first embodiment of the present invention. In this example, of the three shock-absorbing pieces 36, 36 b that are layered in the axial direction to form the shock-absorbing member 18 e, the shape and number of swollen sections 39 c, 39 d that are formed on the shock-absorbing piece 36 b that is arranged in the center in the axial direction differ from in the fourth example of the first embodiment.

In this example, two each of swollen sections 39 c, 39 d that protrude out in the circumferential direction are provided on both side surfaces in the circumferential direction of the held pieces 37 a, 37 b of the shock-absorbing piece 36 b. More specifically, two swollen sections 39 c that are separated from each other are provided in portions near the inner diameter and portions near the outer diameter on one side surface in the circumferential direction of the held pieces 37 a, 37 b, two swollen sections 39 d that are separated from each other are provided in portions near the inner diameter and portions near the outer diameter on the other side surface in the circumferential direction of the held pieces 37 a, 37 b. Moreover, the cross-sectional shape of the swollen sections 39 c, 39 d is an arc shape or D shape on the side surfaces in the circumferential direction.

In this example, each of the two swollen sections 39 c, 39 d are provided so as to be separated from each other, so these swollen sections 39 c, 39 d can elastically deform independently. Therefore, adjustment of the elastic can be performed easily, and it is possible to obtain a more stable elastic force. The other construction and effects are the same as in the second to fourth examples of the first embodiment.

Sixth Example of First Embodiment

FIG. 16 and FIG. 17 illustrate a sixth example of the first embodiment of the present invention. The feature of this example is that, of the shock-absorbing pieces 36, 36 c that are layered in the axial direction to form the shock-absorbing member 18 f, the shock-absorbing piece 36 c that is arranged in the center in the axial direction is integrated with the main damper section 35 a of the damper member 26 a.

The damper member 26 a has a metal circular column shaped support-column section 34 a, and a cylindrical shaped main damper section 35 a that is made of an elastic material such as rubber, an elastomer or the like and that fits around the middle section in the axial direction of the support-column section 34 a so as to be able to displace in the axial direction. The main damper section 35 a is integrally formed with the shock-absorbing piece 36 c such that the outer circumferential surface of the middle section in the axial direction of the main damper section 35 a and the continuous sections between held pieces 37 a, 37 b of the shock-absorbing piece 36 c are continuous at four locations that are uniformly separated in the circumferential direction. This shock-absorbing piece 36 c and the main damper section 35 a having this kind of integrated construction are formed at the same time by injection molding.

In this example as well, the dimension in the axial direction of the main damper section 35 a is set to be greater than the dimension in the axial direction of the shock-absorbing member 18 f and the drive-side arm sections 21 b and the driven-side arm sections 23 b. Therefore, the main damper section 35 a is held in the axial direction between the surfaces of the drive-side base section 20 a and the driven-side base section 22 a that face each other. Moreover, the support-column section 34 a is such that the end sections loosely fit inside the drive-side serration hole 27 and the driven-side serration hole 28.

In this example, the main damper section 35 a of the damper member 26 a and the shock-absorbing pieces 36 a of the shock-absorbing member 18 f are integrally formed, so when compared with the case in which these members are independently formed, it is possible to reduce the number of parts and reduce the accompanying costs, and it is also possible to reduce the number of manufacturing and assembly steps and reduce the accompanying costs. Moreover, the installation position of the main damper section 35 a is regulated by the shock-absorbing member 18 f (shock-absorbing piece 36 c), so it is possible to stabilize the function for absorbing the thrust force that is demonstrated by the damper member 26 a. In this example, it is possible to regulate the installation position of the damper member 26 a by using the shock-absorbing member 18 f, so it is also possible to eliminate the support-column section 34 a from the damper member 26 a. The other construction and effects are the same as in the fourth and fifth example of the first embodiment.

Seventh Example of First Embodiment

FIG. 18 illustrates a seventh example of the first embodiment of the present invention. In this example, the shock-absorbing member 18 g of the torque transmission joint 15 e is constructed by layering in the axial direction three shock-absorbing pieces 36 d, 36 d having a shape in which the shock-absorbing member 18 a that was used in the first example of the first embodiment is divided into three. Each of these shock-absorbing pieces 36 d, 36 e have: held pieces 37 c, 37 d (four held pieces 37 c and four held pieces 37 d) that are layered in the axial direction to form the held sections 25 a, 25 b; outer-diameter side cover pieces 38 a that are layered in the axial direction to form the outer-diameter side cover sections 31; and inner-diameter side cover pieces 40 that are layered in the axial direction to form the inner-diameter side cover sections 32.

In this example as well, when compared with the pair of shock-absorbing pieces 36 d that are arranged on both sides in the axial direction, the shock-absorbing piece 36 e that is arranged in the center in the axial direction is manufactured using a material that elastically deforms more easily. More specifically, together with manufacturing the shock-absorbing piece 36 e using a material that elastically deforms easily such as rubber or an elastomer, the shock-absorbing pieces 36 d are manufactured using a synthetic resin such as polyacetal resin or polyamide resin for which elastic deformation is more difficult than rubber or an elastomer.

Moreover, one each of swollen sections 39 a, 39 b that protrude outward in the circumferential direction are provided on both side surfaces in the circumferential direction of the held pieces 37 c, 37 d of the shock-absorbing piece 36 e. In this example as well, the cross-sectional shape of these swollen sections 39 a, 39 b are a right triangular shape; and of these swollen sections 39 a, 39 b, the side with the large protruding amount in the circumferential direction is located on the outer-diameter side of the held pieces 37 c, 37 d.

In this example, as in the fourth example of the first embodiment, it is possible to increase the damper effect, and it is also possible to prevent looseness of the shock-absorbing member 18 g. Instead of the swollen section 39 a, 39 b having the construction of this example, it is also possible to employ the swollen sections 39 c, 39 d having the construction of the fifth example of the first embodiment, or as in the case of the sixth example of the first embodiment, the shock-absorbing piece 36 e can be integrally formed with the main damper section 35 of the damper member 26. The other construction and effects are the same as in the first example and fourth example of the first embodiment.

Eighth Example of First Embodiment

FIG. 19 illustrates an eighth example of the first embodiment of the present invention. In this example, the shock-absorbing member 18 h of the torque transmission joint 15 f is constructed by layering in the axial direction three shock-absorbing pieces 36 f, 36 g having a shape in which the shock-absorbing member 18 c that was used in the third example of the first embodiment is divided into three. Each of these shock-absorbing pieces 36 f, 36 g have: held pieces 37 e, 37 f (four held pieces 37 e and four held pieces 37 f) that are layered in the axial direction to form the held sections 25 e, 25 f, outer-diameter side cover pieces 38 b that are layered in the axial direction to form the outer-diameter side cover sections 31 b, and inner-diameter side cover pieces 40 a that are layered in the axial direction to form the inner-diameter side cover sections 32 a.

In this example as well, when compared with the pair of shock-absorbing pieces 36 f that are arranged on both sides in the axial direction, the shock-absorbing piece 36 g that is arranged in the center in the axial direction is manufactured using a material that elastically deforms more easily. More specifically, together with manufacturing the shock-absorbing piece 36 g using a material that elastically deforms easily such as rubber or an elastomer, the shock-absorbing pieces 36 f are manufactured using a synthetic resin such as polyacetal resin or polyamide resin for which elastic deformation is more difficult than rubber or an elastomer.

Moreover, one each of swollen sections 39 a, 39 b that protrude outward in the circumferential direction are provided on both side surfaces in the circumferential direction of the held pieces 37 e, 37 f of the shock-absorbing piece 36 g. In this example as well, the cross-sectional shape of these swollen sections 39 a, 39 b is a right triangular shape; and of these swollen sections 39 a, 39 b, the side with the large protruding amount in the circumferential direction is located on the outer-diameter side of the held pieces 37 e, 37 f.

In this example, as in the fourth example of the first embodiment, it is possible to increase the damper effect, and it is also possible to prevent looseness of the shock-absorbing member 18 h. Instead of the swollen section 39 a, 39 b having the construction of this example, it is also possible to employ the swollen sections 39 c, 39 d having the construction of the fifth example of the first embodiment, or as in the case of the sixth example of the first embodiment, the shock-absorbing piece 36 g can be integrally formed with the main damper section 35 of the damper member 26. The other construction and effects are the same as in the third example and fourth example of the first embodiment.

In this first embodiment, in the fourth example to the eighth example, the shock-absorbing member has three shock-absorbing pieces, however, the number of shock-absorbing pieces is not limited to this, and it is possible to construct the shock-absorbing member using two shock-absorbing pieces, or it is also possible to construct the shock-absorbing member using four or more shock-absorbing pieces. It is possible to manufacture all of these shock-absorbing pieces of the shock-absorbing member using the same material, and it is also possible to manufacture all of these shock-absorbing pieces using mutually different materials. Moreover, the cross-sectional shape of the swollen sections is not limited to a right triangular shape or D shape, and it is possible to use various shapes such as a semi-circular shape or a trapezoidal shape. Furthermore, this first embodiment can be embodied using a suitable combination of the construction of each of the examples.

Example of Second Embodiment

FIG. 20 to FIG. 35 illustrate an example of a second embodiment of the present invention. The torque transmission joint of this example has: a drive-side transmission member 16 d that is supported by the tip-end section of an output shaft 12 a as a drive shaft so as to be concentric with the tip-end section and not to rotate relative to the tip-end section; a driven-side transmission member 17 that is supported by the base-end section of a worm shaft 6 a as a driven shaft so as to be concentric with the base-end section and not to rotate relative to the base-end section; a shock-absorbing member 18 i that is provided between the drive-side transmission member 16 d and the driven-side transmission member 17 d; and a damper member 26 b.

The drive-side transmission member 16 d is made of metal and has a drive-side base section 20 b, and four drive-side arm sections 21 c. A drive-side serration hole 27 that engages with a serration fit with a male serration section that is formed around the outer circumferential surface of the tip-end section of the output shaft 12 a is formed in the center section of the drive-side base section 20 b. Moreover, the drive-side arm sections 21 c are provided intermittently in the circumferential direction (spaced at a phase of every 90 degrees) in portions near the outer diameter on a surface of the drive-side base section 20 b that faces the driven-side transmission member 17 d, and protrude out in the axial direction.

On the other hand, the driven-side transmission member 17 d is made of metal and has a driven-side base section 22 b, and four driven-side arm sections. A drive-side serration hole 28 that engages with a serration fit with a male serration section that is formed around the outer circumferential surface of the base-end section of the worm shaft 6 a is formed in the center section of the driven-side base section 22 b. Moreover, the drive-side arm sections 23 c are provided intermittently in the circumferential direction (spaced at a phase of every 90 degrees) in portions near the outer diameter on a surface of the driven-side base section 22 b that faces the drive-side transmission member 16 d, and protrude out in the axial direction. The dimension in the axial direction of the drive-side arm sections 21 c and the dimension in the axial direction of the driven-side arm sections 23 c are the same.

In this example, paired side surfaces 29 g, 29 h in the circumferential direction of the drive-side arm sections 21 c, which are ones of the arm sections 21 c, 23 c, are not arranged in the radial direction, but are arranged so as to incline with respect to the radial direction. More specifically, when the direction of rotation of the output shaft 12 a is in the clockwise direction in FIG. 25, the side surfaces 29 g in the circumferential direction, which are ones of the side surfaces 29 g, 29 h, that are located on the front side in the direction of rotation are inclined toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction (inclined toward the rear in the direction of rotation as going toward the inside in the radial direction). On the other hand, when the direction of rotation of the output shaft 12 a is in the counterclockwise direction in FIG. 25, the side surfaces 29 h in the circumferential direction, which are the others of the side surfaces 29 g, 29 h, that are on the front side in the direction of rotation are inclined toward the front in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction (inclined toward the rear in the direction of rotation as going toward the inside in the radial direction). Moreover, the angle that is formed between the paired side surfaces 29 g, 29 h in the circumferential direction of the drive-side arm sections 21 c is 90 degrees or more (approximately 110 degrees in the example in the figure).

Furthermore, in this example, paired side surfaces 30 g, 30 h in the circumferential direction of the driven-side arm sections 23 c, which are the others of the arm sections 21 c, 23 c, are not arranged in the radial direction, but are arranged so as to incline with respect to the radial direction. More specifically, when the direction of rotation of the output shaft 12 a is in the clockwise direction in FIG. 25, the side surfaces 30 g in the circumferential direction, which are ones of the side surfaces 30 g, 30 h, that are on the front side in the direction of rotation are inclined toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. On the other hand, when the direction of rotation of the output shaft 12 a is in the counterclockwise direction in FIG. 25, the side surfaces 30 h in the circumferential direction, which are the others of the side surfaces 30 g, 30 h, that are on the front side in the direction of rotation are inclined toward the rear in the direction of rotation with respect to the radial direction as going toward the outside in the radial direction. Moreover, the spacing in the circumferential direction between the paired side surfaces 30 g, 30 h in the circumferential direction of the driven-side arm sections 23 c is tapered, or in other words, becomes smaller going toward the outside in the radial direction.

The shock-absorbing member 18 i is constructed by laminating in the axial direction three shock-absorbing pieces 41, 42 (one inside shock-absorbing piece 41, and two outside shock absorbing pieces 42) that have each a cross cylindrical shape, and has eight held sections 43 a, 43 b and four outer-diameter side cover sections 44.

The held sections 43 a, 43 b have a flat plate shape, and are placed between the side surfaces in the circumferential direction of the drive-side arm sections 21 c and the driven-side arm sections 23 c that are adjacent to each other in the circumferential direction. In this example, the paired held sections 43 a, 43 b that are adjacent to each other in the circumferential direction are arranged so as to each have a mirror symmetry about an imaginary plane passing through the center axis of the shock-absorbing member 18 i that exists between each of the paired held sections 43 a, 43 b (planes on the chain lines α, β, γ and δ in FIG. 28) and are inclined in a direction toward each other and toward the imaginary plane with respect to the radial direction as going toward the outside in the radial direction, and therefore the paired held sections 43 a, 43 b are not arranged in the radial direction, but are inclined with respect to the radial direction (the directions of inclination are opposite and the inclination angles are the same between the paired held sections 43 a, 43 b). Combined held sections 45 that are formed from the paired held sections 43 a, 43 b are arranged at four locations that are uniformly spaced in the circumferential direction.

The outer-diameter cover sections 44 each have an outer circumferential shape that is a partial cylindrical shape, and make the outer-diameter side end sections of the paired held sections 43 a, 43 b that are adjacent to each other in the circumferential direction of the combined held sections 45 continuous. On the other hand, the inner-diameter side end section of the non-paired held sections 43 a, 43 b that are adjacent in the circumferential direction but pertain to the different combined held sections 45 are directly continuous. As a result, portions where the outer-diameter side end sections of the held sections 43 a, 43 b that are adjacent to each other in the circumferential direction are made continuous by way of the outer-diameter side cover sections 44, and portions where the inner-diameter side end sections of the held sections 43 a, 43 b are directly made continuous are arranged in an alternating sequence in the circumferential direction. With this kind of construction, the cross-sectional shape of the shock-absorbing member 18 i has a cross cylindrical shape.

Moreover, in this example, of the three shock-absorbing pieces 41, 42 of the shock-absorbing member 18 i, the inside shock-absorbing piece 41 that is located in the center in the axial direction is manufactured using a material that elastically deforms more easily than the shock-absorbing pieces 42 that are located on both sides in the axial direction. More specifically, the inside shock-absorbing piece 41 is manufactured using a material such as rubber or an elastomer that elastically deforms easily, and the outside shock-absorbing pieces 42 are manufactured using a synthetic resin such as polyacetal resin or polyamide resin for which elastic deformation is more difficult than rubber or an elastomer.

In a state that the shock-absorbing member 18 i is assembled, the inside shock-absorbing piece 41 has inside held pieces 46 a, 46 b that constitute the held sections 43 a, 43 b, and inside cover pieces 47 that constitute the outer-diameter side cover sections 44. In the state that the shock-absorbing member 8 i is assembled, the outside shock-absorbing pieces 42 also have outside held pieces 48 a, 48 b that constitute the held sections 43 a, 43 b, and outside cover pieces 49 that constitute the outer-diameter side cover sections 44. Therefore, the held sections 43 a, 43 b of the shock-absorbing member 18 i are constructed by layering in the axial direction the inside held pieces 46 a, 46 b and the outside held pieces 48 a, 48 b, and the outer-diameter side cover sections 44 are constructed by layering in the axial direction the inside cover pieces 47 and the outside cover pieces 49.

The width dimensions (width dimensions in the circumferential direction) of the inside held pieces 46 a, 46 b of the inside shock-absorbing pieces 41 are larger than the width dimensions (width dimensions in the circumferential direction) of the outside held pieces 48 a, 48 b of the outside shock-absorbing pieces 42. As a result, when the shock-absorbing member 18 i is assembled, both side surfaces in the circumferential direction of the inside held pieces 46 a, 46 b protrude further out in the circumferential direction than both side surfaces in the circumferential direction of the outside held pieces 48 a, 48 b, to form swollen sections 50 a, 50 b in those portions. When the shock-absorbing member 18 i and the drive-side arm sections 21 c and driven-side arm sections 23 c are assembled, the swollen sections 50 a, 50 b are elastically compressed a little between the side surfaces 29 g, 29 h in the circumferential direction of the drive-side arm sections 21 c and the side surfaces 30 g, 30 h in the circumferential direction of the driven-side arm sections 23 c. In this example, the width dimensions of the swollen sections 50 a, 50 b are constant over the length direction of the held sections 43 a, 43 b.

In this example, the inside shock-absorbing pieces 41 are integrally formed with the damper member 26 b. The damper member 26 b has a solid circular column shape, and is integrally provided on the inside of the inside shock-absorbing piece 41 by connecting four positions that are uniformly spaced in the circumferential direction of a thin annular connecting section 51 that is formed at a portion near one end in the axial direction on the outer circumferential surface of the damper member 26 b to the continuous sections of the inner-diameter end sections of the inside held pieces 46 a, 46 b respectively. Moreover, the damper member 26 b is such that the other end section in the axial direction (right end in FIG. 31) protrudes to the outside much further in the axial direction than the side surfaces in the axial direction of the inside shock-absorbing piece 41 (and shock-absorbing member 18 i). The inside shock-absorbing piece 41 and the damper member 26 b having this kind of integrated construction are formed at the same time by injection molding.

Moreover, in order to improve the ability to assemble and handle the shock-absorbing member 18 i that is constructed by the three shock-absorbing pieces 41, 42, the inside shock-absorbing piece 41 and the outside shock-absorbing pieces 42 have snap-fit joining construction, and are removably connected to each other. In order for this, hook-shaped locking tabs pieces 52 and concave locking sections 53 are formed on the four outside cover pieces of the outside shock-absorbing pieces 42 so as to be arranged in an alternating sequence in the circumferential direction. The locking tab pieces 52 correspond to locking sections, and the concave locking sections 53 correspond to locked sections, however, instead of locking tab pieces 52 and concave locking sections 53, it is also possible to employ other means for forming locking sections and locked sections.

The locking tab pieces 52 are formed on the inner-diameter side end section of one side surface in the axial direction of the outside cover pieces 49 so as to protrude in the axial direction. The tip-end sections of the locking tab pieces 52 are bent toward the outside in the radial direction. On the other hand, the concave locking sections 54 are formed on the other side surface of the outside cover pieces 49 in the whole radial direction. Moreover, concave grooves 54 through which the locking tab pieces 52 pass are formed on the inner circumferential surfaces of the outside cover pieces 49 where the concave locking sections 53 are formed in the other side surfaces in the axial direction.

When joining the inside shock-absorbing piece 41 and the outside shock-absorbing pieces 42, the outside shock-absorbing pieces 42 are arranged in a state that the one side surfaces in the axial direction of the outside shock-absorbing pieces 42 are made to face each other on both sides in the axial direction of the inside shock-absorbing piece 41, and that the outside shock-absorbing pieces 42 are shifted with respect to each other by a phase of 90 degrees. As a result, at four locations in the circumferential direction, the locking tab pieces 52 and the concave locking sections 53 (concave grooves 54) are located on the same virtual lines. Then, by bringing the outside shock-absorbing pieces 42 toward each other, the locking tab pieces 52 pass through the inside in the radial direction of the inside cover pieces 47 of the inside shock-absorbing piece 41 and the inside of the concave grooves 54 while elastically deforming inward in the radial direction. With the inside shock-absorbing piece 41 elastically deformed a little in the axial direction, the locking tab pieces 52 are elastically restored outward in the radial direction, and the tip-end sections of these locking tab pieces 52 elastically lock in the concave locking sections 53. In this example, by using this kind of snap-fit type of joining construction, the inside shock-absorbing piece 41 and outside shock-absorbing pieces 42 are joined together to form the shock-absorbing member 18 i.

Moreover, the shock-absorbing member 18 i, the drive-side arm sections 21 c and the driven-side arm sections 23 c are combined as illustrated in FIG. 25. More specifically, the driven-side arm sections 23 c (others of the arm sections 21 c, 23 c) are placed on the outside portions in the radial direction of the annular connecting section 51 between the paired held sections 43 a, 43 b of the combined held sections 45. The drive-side arm sections 21 c (ones of the arm sections 21 c, 23 c) are placed between the combined held sections 45 that are adjacent to each other in the circumferential direction (between the non-paired held sections 43 a, 43 b that are adjacent to each other in the circumferential direction but pertain to the different combined held sections 45). As a result, the outer circumferential side surfaces of the driven-side arm sections 23 c are covered by the outer-diameter side cover sections 44 of the shock-absorbing member 18 i. In this state, the paired side surfaces 29 g, 29 h in the circumferential direction of the drive-side arm sections, and the paired side surfaces 30 g, 30 h in the circumferential direction of the driven-side arms sections 23 c face to and come in contact over the entire surface with the side surfaces in the circumferential direction of the held sections 43 a, 43 b in the circumferential direction. The swollen sections 50 a, 50 b are also elastically compressed a little.

Moreover, as illustrated in FIG. 20, with the torque transmission joint 15 g in the assembled state, the damper member 26 is held in the axial direction between the tip-end surface of the output shaft 12 a of the electric motor 8 and the base-end surface of the worm shaft 6 a.

Even in the case of the torque transmission joint 15 g and electric power steering apparatus of this example, it is possible to effectively absorb error such as dimension error or assembly error of components, and it is possible to improve the work efficiency of the inspection process in order to prevent the assembly of the shock-absorbing member 18 i from being forgotten. Furthermore, in this example, the inside shock-absorbing piece 41 and the outside shock-absorbing pieces 42 are joined by snap-fit type joining construction that uses the locking tab pieces 52 and the concave locking sections 53, so it is possible to assemble the shock-absorbing member 18 i easily, and to improve the ability to handling the shock-absorbing member 18 i. The other construction and effects are the same as in the case of the torque transmission joint and electric power steering apparatus of the first embodiment.

In regards to the shape of the swollen sections, construction is not limited to a shape in which the width dimension does not change in the length direction of the held sections, and the construction illustrated in FIGS. 36A and 36B can also be used. In other words, as illustrated in FIG. 36A, the width dimensions (amount of swelling) of the swollen sections 50 c, 50 d can become greater as going toward the outer-diameter side of the held sections 43 a, 43 b such that these swollen sections 50 c, 50 d have a triangular shape, or as illustrated in FIG. 36B, the width dimensions (amount of swelling) of the swollen sections 50 e, 50 f can become greater as going toward the center in the length direction of the held sections 43 a, 43 b such that these swollen sections 50 e, 50 f have a convex arc shape. When employing this kind of construction, the elastic force demonstrated by the swollen sections 50 c (50 e), 50 d (50 f) gradually increases, so it is possible to more gently increase the transmission torque.

In this example, with an intention of reducing costs by making parts common, the shapes of the pair of outside shock-absorbing pieces are the same, however, for example, it is also possible to use a pair of outside shock-absorbing pieces that have different shapes, such as forming four locking tab pieces on the outside shock-absorbing piece on one side, and forming four concave locking sections in the outside shock-absorbing piece on the other side.

In either embodiment, a drive-side transmission member having the same shape as the driven-side transmission member shown in the above examples can be attached to the tip-end section of the output shaft of the electric motor, and a driven-side transmission member having the same shape as the drive-side transmission member shown in the above examples can be attached to the base-end section of the work shaft. That is, in the embodiments of the present invention, the drive-side transmission member and the driven-side transmission member can be interchangeably used.

INDUSTRIAL APPLICABILITY

The torque transmission joint of the present invention can particularly be suitably applied to an electric power steering apparatus for an automobile, however, can also be widely used in various kinds of machinery having construction in which torque is transmitted between a drive shaft and a driven shaft.

EXPLANATION OF REFERENCE NUMBERS

-   1 Steering wheel -   2 Steering shaft -   3 Housing -   4 Worm wheel -   5 Worm -   6, 6 a Worm shaft -   7 Worm teeth -   8 Electric motor -   9 a, 9 b Rolling bearing -   10 Pressure piece -   11 Coil spring -   12, 12 a Output shaft -   13 Spline hole -   14 Spline shaft section -   15, 15 a to 15 g Torque transmission joint -   16, 16 a to 16 d Drive-side transmission member -   17, 17 a to 17 d Driven-side transmission member -   18, 18 a to 18 i Shock-absorbing member -   19 Steel ball -   20, 20 a, 20 b Drive-side base section -   21, 21 a to 21 c Drive-side arm section -   22, 22 a, 22 b Driven-side base section -   23, 23 a to 23 c Driven-side arm section -   24 Cylindrical section -   25, 25 a to 25 f Held section -   26, 26 a, 26 b Damper member -   27 Drive-side serration hole -   28 Driven-side serration hole -   29 a to 29 h Side surface in the circumferential direction -   30 a to 30 h Side surface in the circumferential direction -   31, 31 a to 31 c Outer-diameter side cover section -   32, 32 a Inner-diameter side cover section -   33, 33 a, 33 b Combined held section -   34, 34 a Support column section -   35, 35 a Main damper section -   36, 36 a to 36 g Shock-absorbing piece -   37 a to 37 f Held piece -   38, 38 a, 38 b Outer-diameter side cover piece -   39 a to 39 d Swollen section -   40, 40 a Inner-diameter side cover piece -   41 Inside shock-absorbing piece -   42 Outside shock-absorbing piece -   43 a, 43 b Held section -   44 Outer-diameter side cover section -   45 Combined held section -   46 a, 46 b Inside held piece -   47 Inside cover piece -   48 a, 48 b Outside held piece -   49 Outside cover piece -   50 a to 50 f Swollen section -   51 Annular connecting section -   52 Locking tab piece -   53 Concave locking section -   54 Concave groove 

What is claimed is:
 1. A torque transmission joint comprising: a drive-side transmission member supported by an end section of a drive shaft concentrically with the drive shaft; a driven-side transmission member supported by an end section of a driven shaft concentrically with the driven shaft and, arranged in series with the drive-side transmission member in an axial direction of the torque transmission joint; and a shock-absorbing member made of an elastic material and provided between the drive-side transmission member and the driven-side transmission member; the torque transmission joint transmitting torque between the end sections of the drive shaft and the driven shaft; wherein the drive-side transmission member comprises: a drive-side base section supported by the end section of the drive shaft, and having a surface facing the driven-side transmission member; and a plurality of drive-side arm sections provided on the surface of the drive-side base section intermittently in a circumferential direction of the torque transmission joint so as to protrude out in the axial direction, and each of the drive-side arm sections having paired side surfaces in the circumferential direction; the driven-side transmission member comprises: a driven-side base section supported by the end section of the driven shaft, and having a surface facing the drive-side transmission member; and a plurality of driven-side arm sections provided on the surface of the driven-side base section intermittently in the circumferential direction so as to protrude out in the axial direction, and each of the driven-side arm sections having paired side surfaces in the circumferential direction; the shock-absorbing member comprises combined held sections located at plural locations of the shock-absorbing member in the circumferential direction, the combined held sections comprising adjacent paired flat plate shaped held sections, inner-diameter side end sections of each of the paired flat plate shaped held sections being connected to each other directly or by an inner-diameter side cover section; and outer-diameter cover sections connecting outer-diameter side end sections of adjacent non-paired flat plate shaped held sections between the adjacent combined held sections, such that the held sections are connected on the inner-diameter side and the outer-diameter side alternately in the circumferential direction, and the shock-absorbing member being constructed so as to have a non-circular tube shape in a cross section thereof; the drive-side arm sections and the driven-side arm sections are arranged in an alternating sequence in the circumferential direction, and the held sections are respectively arranged between the side surfaces of the drive-side arm sections and the driven-side arm sections that are adjacent to each other in the circumferential direction; arm sections of one of the pluralities of arm sections being placed between the paired held sections, respectively, and arm sections of another of the pluralities of arm sections being places between the non-paired held sections, respectively, and outer circumferential surfaces of either of the drive-side arm sections or the driven-side arm sections are covered by the outer-diameter side cover sections which are exposed to an outside of the torque transmission joint; and the shock-absorbing member is formed from two or more shock-absorbing pieces, including at least two types of shock-absorbing pieces with different elasticities, and the shock-absorbing pieces have held pieces that form the held sections; and cover pieces that form the outer-diameter side cover sections, with the shock-absorbing pieces layered in the axial direction.
 2. The torque transmission joint according to claim 1, wherein side surfaces in the circumferential direction of the held pieces of one of the shock-absorbing pieces which is more elastically deformable than the other shock-absorbing pieces protrude further in the circumferential direction than side surfaces in the circumferential direction of the held pieces of the other shock-absorbing pieces.
 3. The torque transmission joint according to claim 1, wherein the shock-absorbing pieces of the shock-absorbing member are joined together by engagement between an engaging section and an engaged section that are provided on the shock-absorbing pieces.
 4. The torque transmission joint according to claim 1, wherein a damper member for absorbing part of a thrust force that acts between the drive shaft and the driven shaft and transmitting another part of the thrust force that acts between the drive shaft and the driven shaft is provided on an inside of the shock-absorbing member.
 5. The torque transmission joint according to claim 4, wherein the damper member is integrally formed with at least one of the shock-absorbing pieces of the shock-absorbing member.
 6. The torque transmission joint according to claim 1, wherein the combined held sections are provided at four locations of the shock-absorbing member that are uniformly spaced in the circumferential direction, and the non-circular tube shape in the cross section of the shock-absorbing member is a cross cylindrical shape.
 7. An electric power steering apparatus comprising: a housing that is supported by a fixed portion of a vehicle body; a rotating steering shaft that rotates as a steering wheel of the vehicle is rotated and applies a steering angle to steered wheels; a worm wheel that is supported by part of the rotating steering shaft so as to be concentric with the rotating steering shaft, and rotates together with the rotating steering shaft; a worm that comprises a worm shaft both end sections in an axial direction of the worm shaft being supported inside the housing by bearings so as to be able to rotate freely, and a middle section in the axial direction around which worm teeth that engage with the worm wheel are provided; and an electric motor; wherein the torque transmission joint according to claim 1 is provided between an output shaft of the electric motor and the worm shaft such that the torque transmission joint can transmit a torque between the output shaft acting as the drive shaft and the worm shaft acting as the driven shaft.
 8. The torque transmission joint according to claim 1, wherein the paired held sections each have a mirror symmetry about an imaginary plane that passes through a center axis of the torque transmission joint, and are inclined in a direction toward the imaginary plane with respect to a radial direction of the shock-absorbing member going toward an outside in the radial direction of the shock-absorbing member, and the side surfaces of the paired side surfaces of the drive-side arm sections, which are positioned on a front side in a direction of rotation of the drive shaft are inclined in a direction toward the front side in the direction of rotation with respect to the imaginary plane going toward the outside in the radial direction. 